1. Field of the Invention
This invention relates to a process and an apparatus for selective transportation of combustion media gas and air to a heating chamber, where the gas and combustion air are mixed and burned in controlled amounts. To reduce the level of NO.sub.x pollutants contained in the resulting waste gases, the feed is preferably arranged so that the combustion air is introduced into the combustion chamber at different heights to achieve an initially substoichiometric combustion with the lowest possible temperatures at the flame tip. Gases, such as NO/NO.sub.2, accelerate the flame reaction. To compensate for this effect and/or to slow down the flame reaction, waste gas can be introduced. The waste gas or partially combusted gas can be added to and mixed in with the combustion air.
2. Background Information
In ovens where heating chambers are heated by heating flues in the oven walls, uncontrolled flow conditions are a common feature, In some of the known heating chambers, there are pronounced recirculation flows. U.S. Pat. No. 4,412,890 discloses an oven battery that includes heating flues having hollow shaft members formed with orifices at different elevations. The shaft members are connected to regenerators for the supply of preheated gaseous combustion agents. One shaft member is supplied with preheated lean gas, and another shaft is supplied with preheated combustion-supporting air. The shafts are connected to the regenerators. The shafts narrow upwardly in steps. The upwardly-decreasing cross section serves to decrease the quantity of gas issuing from the exit orifices at each orifice further up the flue. On the other hand, the cross sections of the flue chambers widen upwardly in steps to increase the quantity of burning gas. Also, the exit orifices extend inclinedly upwards and inclinedly laterally toward the center of the heating flue to reduce the flow resistance which opposes the flow of gaseous medium issuing and entering through the slots.
Another example of a process for heating the walls of an oven is disclosed in the German Patent No. 391,501, where the speed of the combustion gas stream is increased in the direction of the flow through the heating chamber or flue by the narrowing of the flow path through the flue. In this manner, the transfer of heat to the oven walls is increased.
German Patent No. 655,948 discloses a heating flue for heating the walls of an oven, or the like, in which the flue is divided into separate heating channels by a wall that extends upwardly through the heating flue. The wall includes openings spaced along its length. The gas and air are introduced into the flue on opposite sides of the separating wall. The gas and air flow upwardly on opposite sides of the wall and pass through the wall openings along the length of the wall into a mixture, for combustion of the gas and air to take place. The wall is sloped or inclined from the vertical at the entrance of the heating flue so that the diameters of the gas and air inlets are different from one another. The wall is positioned so that at the exit of the flue, the separate gas and air channels have equal diameters. In this manner, mixing of the gas and air is controlled to achieve uniform heating of the adjacent walls along the length of the heating flue.
While it is known to redistribute preheated gaseous combustion-supporting agents and preheated lean gas by varying the cross section of the shafts and chambers supplying the combustion media, there is a need for a heating chamber apparatus that effectively controls the flow of gas, air and products of combustion therethrough over a specified distance to achieve controlled combustion in the combustion chamber.